/*
 * Label.java July 2006
 *
 * Copyright (C) 2006, Niall Gallagher <niallg@users.sf.net>
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * permissions and limitations under the License.
 */

package wx.xml.simpleframework.xml.core;

import java.lang.annotation.Annotation;

import wx.xml.simpleframework.xml.strategy.Type;

/**
 * The <code>Label</code> interface is used to describe an reference to
 * a field annotated with an XML schema annotation. Because each field
 * and annotation is different, there are different ways in which the
 * annotation can be accessed. This provides a uniform means for
 * accessing the field annotation details and the field properties.
 * <p>
 * This also exposes a <code>Converter</code> object, which is used to
 * convert an XML node into a property that can be assigned to the
 * annotated field. Each converter returned is specific to the label
 * and knows, based on the annotation, how to serialize the field.
 *
 * @author Niall Gallagher
 */
interface Label {

    /**
     * This is used to acquire the <code>Decorator</code> for this.
     * A decorator is an object that adds various details to the
     * node without changing the overall structure of the node. For
     * example comments and namespaces can be added to the node with
     * a decorator as they do not affect the deserialization.
     *
     * @return this returns the decorator associated with this
     */
    Decorator getDecorator() throws Exception;

    /**
     * This is used to acquire the <code>Type</code> that the type
     * provided is represented by. Typically this will return the
     * field or method represented by the label. However, in the
     * case of unions this will provide an override type.
     *
     * @param type this is the class to acquire the type for
     * @return this returns the type represented by this class
     */
    Type getType(Class type) throws Exception;

    /**
     * This is used to acquire the <code>Label</code> that the type
     * provided is represented by. Typically this will return the
     * same instance. However, in the case of unions this will
     * look for an individual label to match the type provided.
     *
     * @param type this is the type to acquire the label for
     * @return this returns the label represented by this type
     */
    Label getLabel(Class type) throws Exception;

    /**
     * This returns a <code>Collection</code> of element names. This
     * will typically contain both the name and path of the label.
     * However, if this is a union it can contain many names and
     * paths. This method should never return null.
     *
     * @return this returns the names of each of the elements
     */
    String[] getNames() throws Exception;

    /**
     * This returns a <code>Collection</code> of element paths. This
     * will typically contain only the path of the label, which is
     * composed using the <code>Path</code> annotation and the name
     * of the label. However, if this is a union it can contain many
     * paths. This method should never return null.
     *
     * @return this returns the names of each of the elements
     */
    String[] getPaths() throws Exception;

    /**
     * This is used to provide a configured empty value used when the
     * annotated value is null. This ensures that XML can be created
     * with required details regardless of whether values are null or
     * not. It also provides a means for sensible default values.
     *
     * @param context this is the context object for the serialization
     * @return this returns the string to use for default values
     */
    Object getEmpty(Context context) throws Exception;

    /**
     * This method returns a <code>Converter</code> which can be used to
     * convert an XML node into an object value and vice versa. The
     * converter requires only the context object in order to perform
     * serialization or deserialization of the provided XML node.
     *
     * @param context this is the context object for the serialization
     * @return this returns an object that is used for conversion
     */
    Converter getConverter(Context context) throws Exception;

    /**
     * This is used to acquire the name of the element or attribute
     * that is used by the class schema. The name is determined by
     * checking for an override within the annotation. If it contains
     * a name then that is used, if however the annotation does not
     * specify a name the the field or method name is used instead.
     *
     * @return returns the name that is used for the XML property
     */
    String getName() throws Exception;

    /**
     * This is used to acquire the path of the element or attribute
     * that is used by the class schema. The path is determined by
     * acquiring the XPath expression and appending the name of the
     * label to form a fully qualified path.
     *
     * @return returns the path that is used for the XML property
     */
    String getPath() throws Exception;

    /**
     * This method is used to return an XPath expression that is
     * used to represent the position of this label. If there is no
     * XPath expression associated with this then an empty path is
     * returned. This will never return a null expression.
     *
     * @return the XPath expression identifying the location
     */
    Expression getExpression() throws Exception;

    /**
     * This returns the dependent type for the annotation. This type
     * is the type other than the annotated field or method type that
     * the label depends on. For the <code>ElementList</code> and
     * the <code>ElementArray</code> this is the component type that
     * is deserialized individually and inserted into the container.
     *
     * @return this is the type that the annotation depends on
     */
    Type getDependent() throws Exception;

    /**
     * This is used to either provide the entry value provided within
     * the annotation or compute a entry value. If the entry string
     * is not provided the the entry value is calculated as the type
     * of primitive the object is as a simplified class name.
     *
     * @return this returns the name of the XML entry element used
     */
    String getEntry() throws Exception;

    /**
     * This is the key used to represent this label. The key is used
     * to store the parameter in hash containers. Typically the
     * key is generated from the paths associated with the label.
     *
     * @return this is the key used to represent the label
     */
    Object getKey() throws Exception;

    /**
     * This acquires the annotation associated with this label. This
     * is typically the annotation acquired from the field or method.
     * However, in the case of unions this will return the actual
     * annotation within the union group that this represents.
     *
     * @return this returns the annotation that this represents
     */
    Annotation getAnnotation();

    /**
     * This is used to acquire the contact object for this label. The
     * contact retrieved can be used to set any object or primitive that
     * has been deserialized, and can also be used to acquire values to
     * be serialized in the case of object persistence. All contacts
     * that are retrieved from this method will be accessible.
     *
     * @return returns the field that this label is representing
     */
    Contact getContact();

    /**
     * This acts as a convenience method used to determine the type of
     * the field this represents. This is used when an object is written
     * to XML. It determines whether a <code>class</code> attribute
     * is required within the serialized XML element, that is, if the
     * class returned by this is different from the actual value of the
     * object to be serialized then that type needs to be remembered.
     *
     * @return this returns the type of the field class
     */
    Class getType();

    /**
     * This is used to acquire the name of the element or attribute
     * as taken from the annotation. If the element or attribute
     * explicitly specifies a name then that name is used for the
     * XML element or attribute used. If however no overriding name
     * is provided then the method or field is used for the name.
     *
     * @return returns the name of the annotation for the contact
     */
    String getOverride();

    /**
     * This is used to determine whether the annotation requires it
     * and its children to be written as a CDATA block. This is done
     * when a primitive or other such element requires a text value
     * and that value needs to be encapsulated within a CDATA block.
     *
     * @return this returns true if the element requires CDATA
     */
    boolean isData();

    /**
     * Determines whether the XML attribute or element is required.
     * This ensures that if an XML element is missing from a document
     * that deserialization can continue. Also, in the process of
     * serialization, if a value is null it does not need to be
     * written to the resulting XML document.
     *
     * @return true if the label represents a some required data
     */
    boolean isRequired();

    /**
     * This method is used to determine if the label represents an
     * attribute. This is used to style the name so that elements
     * are styled as elements and attributes are styled as required.
     *
     * @return this is used to determine if this is an attribute
     */
    boolean isAttribute();

    /**
     * This is used to determine if the label is a collection. If the
     * label represents a collection then any original assignment to
     * the field or method can be written to without the need to
     * create a new collection. This allows obscure collections to be
     * used and also allows initial entries to be maintained.
     *
     * @return true if the label represents a collection value
     */
    boolean isCollection();

    /**
     * This is used to determine whether the label represents an
     * inline XML entity. The <code>ElementList</code> annotation
     * and the <code>Text</code> annotation represent inline
     * items. This means that they contain no containing element
     * and so can not specify overrides or special attributes.
     *
     * @return this returns true if the annotation is inline
     */
    boolean isInline();

    /**
     * This is used to determine if the label represents text. If
     * a label represents text it typically does not have a name,
     * instead the empty string represents the name. Also text
     * labels can not exist with other text labels, or elements.
     *
     * @return this returns true if this label represents text
     */
    boolean isText();

    /**
     * This is used to determine if an annotated list is a text
     * list. A text list is a list of elements that also accepts
     * free text. Typically this will be an element list union that
     * will allow unstructured XML such as XHTML to be parsed.
     *
     * @return returns true if the label represents a text list
     */
    boolean isTextList();

    /**
     * This is used to determine if this label is a union. If this
     * is true then this label represents a number of labels and
     * is simply a wrapper for these labels.
     *
     * @return this returns true if the label represents a union
     */
    boolean isUnion();

    /**
     * This is used to describe the annotation and method or field
     * that this label represents. This is used to provide error
     * messages that can be used to debug issues that occur when
     * processing a method. This should provide enough information
     * such that the problem can be isolated correctly.
     *
     * @return this returns a string representation of the label
     */
    String toString();
}
